Genetically we have determined the existence of four genes specifying leucine transport by the LIV-I system. Two of these have been shown to code the LIV and leucine-specific binding proteins. We have cloned a DNA segment containing these genes and have constructed a restriction map of the fragment. The partial DNA sequence of one gene has been determined, with our goal to completely sequence all of the relevant genes. In vitro, transcription and translation of the clone genes has revealed precursor molecules of the binding proteins and has permitted a tentative indentification of the other gene products. We are now engaged in studies of the mechanisms of interaction/secretion of these gene products into membrane, the identification and purification of all lucine transport gene products, and a detailed analysis of regulation of these genes in vitro.